Fingerprints are an important proof aiding and arresting accused offenders and therefore to detecting fingerprints is a very important factor in criminal investigations. Conventional fingerprint detection is carried out in such a manner that aluminum powder is put on the surface of an object to be investigated where fingerprints adhere or on a surface of an object which is considered to have fingerprints adhered to there. The object is swept with a brush to adhere the powder on the latent fingerprints to actualize them; then the actualized fingerprint is printed on a gelatin paper (hereinafter called the "dry powder method").
However, in the conventional dry powder method, if the object to be investigated or the latent fingerprint adhered to on the object is wet, it is impossible to adhere the aluminum powder on to the latent fingerprint to actualize it; in such a case, it is necessary to wait until the object to be investigated, such as a wet window, a wet door, a wet of vehicle body or any other article left on a criminal site, gets dry or to make them dry by using, for example, a dryer. Such processes are complicated, and further the latent fingerprints sometimes disappear in such wet conditions. In this manner, according to the conventional dry powder method, it is very difficult to detect fingerprints, particularly, outside under wet rainy weather.
On the other hand, the conventional dry powder method requires a skill to actualize the latent fingerprint by swiping. Therefore, a non-skilled person sometimes causes damage to the ridged line of the fingerprint to be detected in spite of the wet or dry conditions.
Further, in case the surface of the object to be investigated is large or a large number of the articles are left at a criminal site, the wiping work is so hard because the operator has to wipe them with a brush continuously and very carefully at every small region, for example, 10.times.10 cm square or on every article left at the site.